VRRP and Load Sharing

one or more “backup” Routers against only one “standby” router for HSRP, hence the presence of “skew time” to organize their participation to the election.

can use real IP address as the virtual IP.

use 224.0.0.18, udp(112).

VRRP use the same concept of multiple group to achieve load sharing.

Hold = 3xAdvertisment + skew time.

“Advertisement” , called “Hello” in HSRP.

Skew time = 1-(priority/256).

The skew time is inversely proportional to the priority, the hypothetical topology depicted in figure 1 better illustrates the utility that lurks behind the concept.

Figure1: skew time and priority

The hold time allows backup routers to be aware of a failure of the master for them to be able to send their advertisements and participate to the election of the new master, but with many routers as backup with different priorities it is clear that only the backup router with the highest priority will become the Master, so there is no need for the others to participate to the “masquerade” : ); thereby, using the skew time, only the backup router with the next highest priority will send its advertisements, become the Master and inform all others, if for any reason it is also not available, The next highest priority backup router will claim the master state.

After the hold timer expires for VRRP group 10, MLS is considered down and R2 interface fa1/0.10 take over the Master status and become the forwarder, this is confirmed by the traffic that VLAN10 takes to reach the upstream destination:

R2#sh vrrp briefInterface Grp Pri Time Own Pre State Master addr Group addr

Fa1/0.1010150 3414 Y Master192.168.10.2192.168.10.1

Fa1/0.20 20 200 3218 Y Master 192.168.20.2 192.168.20.1

R2#

R10#trace 10.10.10.1

Type escape sequence to abort.

Tracing the route to 10.10.10.1

1 192.168.10.2 68 msec 44 msec 60 msec

2 192.168.12.1 152 msec 92 msec 92 msec

3 10.10.10.1 136 msec 92 msec 140 msec

R10#

R10#sh arpProtocol Address Age (min) Hardware Addr Type Interface

Internet 192.168.10.2 44 cc01.154c.0010 ARPA FastEthernet0/0

Internet 192.168.10.3 7 cc02.1714.0000 ARPA FastEthernet0/0

Internet 192.168.10.1 7 0000.5e00.010a ARPA FastEthernet0/0

Internet 192.168.10.10 – cc04.1714.0000 ARPA FastEthernet0/0

R10#

Note that the virtual MAC has not changed, because the operation is transparent to the clients.

Nothing changed for VLAN 20, traffic is still forwarded to R2:

R20#trace 10.10.10.1

Type escape sequence to abort.

Tracing the route to 10.10.10.1

1 192.168.20.2 112 msec 76 msec 28 msec

2 192.168.12.1 72 msec 112 msec 64 msec

3 10.10.10.1 136 msec 44 msec 56 msec

R20#

MLS recovery:

Now MLS is back to live and because of the preempt feature it will claim its master status back, however, this is done after a configured 60 seconds, this additional time is given to the downstream Layer 2 distribution swiches to converge STP so the optimal layer 3 path is consistent with layer 2 STP path.